1. Field of the Invention
The present invention relates to a method of manufacturing an organic electroluminescence (EL) display device.
2. Description of the Related Art
A generally known display device having organic EL elements mounted thereon is a device in which pixels each having a single or multiple organic EL elements are arranged in a predetermined pattern. By those pixels, a display region of the display device is two-dimensionally and finely divided. The organic EL elements included in the pixels are electronic elements which output, for example, any one of red light, green light, and blue light. A display device having organic EL elements mounted thereon obtains a full-color image by driving the organic EL elements for outputting desired colors at desired emission intensities.
By the way, in an organic EL element which is a component of a display device, an organic compound layer in the element is a thin film layer formed by forming a thin film made of an organic material by vapor deposition or the like. When the organic compound layer in the organic EL element of the display device is formed for each element by vapor deposition, a fine patterning technology is necessary. Upon performance of the patterning, a fine metal mask the fineness of which is according to the fineness of the patterning is necessary. However, a vapor deposited film which adheres when the metal mask is used repeatedly in vapor deposition may narrow an opening in the mask or stress may deform the opening in the mask. Therefore, it is necessary to clean the mask used after film formation for a fixed number of times, which is a disadvantageous factor from the viewpoint of manufacturing costs. Further, partly due to a limitation on the process accuracy of the mask, the pixel size has a limit of about 100 μm, which is disadvantageous to a finer size. Further, with regard to the substrate size, when a fine metal mask is increased in size, in order to secure the positional accuracy of the opening in the mask, it is necessary to enhance the stiffness of a frame of the mask. However, when the stiffness of the mask is enhanced, an increase in the weight of the mask itself is caused accordingly. Therefore, from the viewpoint of both processability and handling, when large format display devices of the fourth and subsequent generations are to be produced, an optimum production process of a fine organic EL element and a display device having the organic EL element mounted thereon has not taken shape at present.
Under those circumstances, a method of manufacturing a display device having a fine organic EL element without using a metal mask is proposed.
In the method proposed in Japanese Patent No. 3839276, a photoresist is directly formed on an emission layer. When the method is adopted, the photoresist to be used generally contains large amounts of a photoinitiator, a crosslinking agent, and the like. Here, the photoinitiator, the crosslinking agent, and the like are each a material for changing insolubility at least in a developer. In the method proposed in Japanese Patent No. 4507759, an intermediate layer formed of a water-soluble material is provided on an organic compound layer, and the organic compound layer is patterned by performing photolithography on the intermediate layer. Here, a water-soluble polymer for constituting the intermediate layer to be formed on an emission layer is generally insulative. In addition, Japanese Patent No. 4544811 proposes such a technology that a water-soluble polymer is used as a release layer and a photoresist is released together with the release layer.
The resist, the intermediate layer, the release layer, and the like are generally insulative. Accordingly, when any one of those layers is being left on the surface of the emission layer or the like of an organic EL element, the layer serves as a resistance to remarkably deteriorate the element characteristics of the organic EL element in an organic EL display device. Accordingly, the resist, the intermediate layer, the release layer, and the like need to be removed so that none of the layers may remain on the surface of the emission layer or the like. However, it is difficult to completely remove the resist, the intermediate layer, the release layer, and the like each formed of a polymer material, and hence the residue that cannot be completely removed remains in the device to some extent. Further, concern is raised about the deterioration of the element characteristics due to, for example, the following. A trace amount of an impurity in the resist, the intermediate layer, the release layer, or the like, or a solvent to be used upon application of the resist, the intermediate layer, the release layer, or the like diffuses to the emission layer or the like constituting the organic compound layer to cause the crystallization of the organic compound layer. Accordingly, the following problem has conventionally arisen. The element characteristics of an organic EL element in an organic EL display device produced by patterning involving utilizing a photolithography process are inferior to the element characteristics of organic EL elements formed like a pattern with a metal mask or the like in a vacuum in-situ fashion.